Moulding process

ABSTRACT

A highly effective and cost-effective method and apparatus for manufacturing soft contact lenses by physically forming the lenses form sheet (or other solid) material in a batch or continuous process.

This application claims the priority under 35 U.S.C. 371 of prior PCTapplication PCT/GB2005/000107, filed Jan. 13, 2005, which in turn claimsthe priority of prior Great Britain patent application nos. 0400666.4,filed Jan. 13, 2004; 0422966.2, filed Oct. 18, 2004; and 0425105.4,filed Nov. 15, 2004, all of which are incorporated herein in theirentirety by reference.

FIELD OF THE INVENTION

The present invention relates to a method and apparatus for producing aplurality of ophthalmic lenses such as soft contact lenses andophthalmic lenses thus produced.

BACKGROUND ART

The conventional method of producing ophthalmic lenses is to form a lensblank by polymerisation of liquid monomers in a mould and tosubsequently mechanically lathe the lens blank into a finished lens andto polish the lens to remove imperfections. This method islabour-intensive and expensive.

In recent times, double-sided cast moulding (DSCM) processes have beendeveloped. These processes generally involve the initial production (bymoulding) of single-use male and female moulds. Liquid monomers are thendeposited into the female mould and the male and female moulds are matedtogether. The monomers are then cured by heating to form the desiredpolymer lens (the term ‘cured’ means that the material being cured isrendered insoluble in a solvent in which it was previously soluble andthe term is thus a generic term covering more specific terms such aspolymerisation, crosslinking, vulcanisation etc.). The lens is removedfrom the mould and is washed to extract unreacted monomers and/orsolvents. The moulds are then discarded and the lenses are packed infinal packs.

It is to be noted that the controllable moulding process in such a DSCMprocess is the moulding of the single-use moulds rather than that of thelenses themselves. The most common way of producing the single-usemoulds is to produce them between two platens with removably mounted,precisely machined inserts mounted on the platens. A change of mouldshape (in order to produce a lens with different optical qualities) isachieved through a change of inserts in the moulding platen. The insertsare generally created on a precision lathe and are polished to removesurface imperfections. Some particular lens optical qualities arecreated by controlling the orientation of the male to the female mould.

Thus in a DSCM process, it is the shapes of the disposable moulds whichdetermine the shape and power of the final lens.

U.S. Pat. No. 5,508,317 discloses an improvement to standard DSCM inwhich an aqueous solution of prepolymer is introduced into the mould andcuring is effected by photo-crosslinking. It is claimed that this givesthe advantage of allowing the washing/extraction step of standard DSCMto be dispensed with.

Other improvements which have been proposed to DSCM include making oneof the moulds reusable and making at least one of the mouldsUV-transparent to allow UV curing.

WO 98/42497 discloses the curing of lenses produced using a DSCM processby the use of UV alone.

U.S. Pat. Nos. 4,673,539 and 4,786,446 disclose a different productionprocess approach involving creating a shaped thermoplastic hydrogelprecursor by the thermoforming of a particular form of uncrosslinkedpolymer (one containing the product of an ethylenically-unsaturatedmonomer bearing at least one trihaloacetoxy-substitute group),subsequently solvolyzing the precursor in the presence of a diluent inorder to form a polymeric shaped article and finally hydrating theshaped article to provide an ophthalmic lens. This process is claimed toproduce lenses with high and controllable water sorbencycharacteristics.

DSCM processes suffer from problems with quality variation in productioncaused both by control of mould quality in the two-step castingprocedure and by variability in the curing process. In the practicalenvironment of a commercial production process, the curing process isalways subject to variations in monomer mixtures and variations inmonomer mixture components. A practical curing process is also subjectto changes in cure rates due to fluctuations in energy of the (normallythermal) curing source.

All prior art processes suffer from problems of manufacturingefficiency—being, at best, batch processes requiring significant humaninvolvement and, at worst, effectively custom-manufacturing processesrequiring skilled operators for each and every process step. Due tothis, the cost of production of ophthalmic lenses is relatively high.

It is an object of this invention to provide a method for producingophthalmic lenses with improved manufacturing efficiency compared toprior art methods. In particular, the method of the current inventionprovides increased consistency and quality of production as well as areduction in the quantity of process steps required when compared withprior art methods.

It is a further object of this invention to reduce the quantity ofmaterial consumed by the moulding and curing process for an ophthalmiclens and thus, in this way, to reduce the environmental impact of themoulding and curing process.

It is a further object of this invention to also reduce theenvironmental impact of the moulding and curing process by reducing theamount of wet-chemistry and associated chemical waste products whencompared with prior art processes.

SUMMARY OF THE INVENTION

The present invention overcomes the problems mentioned above throughprovision of a method of producing a plurality of soft contact lenses inwhich a solid, substantially dry material is provided, which iswater-soluble above a certain temperature. This material is then formedinto a plurality of shaped lens blanks through controlled application ofphysical force to the material and the shaped lens blanks aresubsequently hydrated at a temperature below the certain temperature(above which the material is water-soluble) to form a plurality of softcontact lenses.

The present invention also provides an apparatus for producing aplurality of soft contact lenses comprising a forming means for applyinga controlled physical force to a sheet of material in order to form aplurality of shaped lens blanks and sheet material transport meanscomprising driven and/or undriven roller means for transporting a sheetof material.

In preferred embodiments of the method provided by the invention, thecertain temperature, above which the material is water-soluble is eitherapproximately 50° C. or approximately 65° C.

In other desirable embodiments of the method of the invention, thematerial may be:

-   -   polyvinyl alcohol or    -   a copolymer of polyvinyl alcohol and polyvinyl acetate or    -   polyethylene-maleic-anhydride or    -   polymethyl-hydroxy-propyl-cellulose or    -   copolymers of methyl acrylate or    -   ethyl acrylate with ethylene or their hydroxy derivatives or    -   a copolymer of polyvinyl alcohol and polyvinyl acetate where the        degree of hydrolysis, as measured by saponification, is at least        96% mol based on the original polyvinyl alcohol.

In a further desirable embodiment of the method of the invention, thematerial is a substantially uncrosslinked polymer comprisingcrosslinkable groups. In this embodiment, prior to the hydration step C,high energy is applied to the shaped lens blanks, crosslinking thepolymer to a predetermined, desired crosslink density. The polymer mayalso contain additives that react to the application of high energy toimprove crosslinking efficiency. ‘High energy’ may be in any of thefollowing forms:

-   -   electron beam irradiation or    -   gamma irradiation or    -   microwave irradiation or    -   ultraviolet irradiation or    -   infrared irradiation or    -   thermal irradiation or    -   ultrasound irradiation.

In a particularly preferred embodiment of the method of the invention,the material is provided in as a sheet of material and the shaped lensblanks remain at least partially attached to this sheet of materialafter the physical forming step B. This allows the sheet to be used as atransport medium/carrying mechanism for the shaped lens blanks. Afurther desirable implementation for such a method is to remove theshaped lens blanks from the sheet, at the appropriate point in theprocess using a laser cutting device.

The physical forming step B may be carried out using a number ofdifferent processes such as:

-   -   thermoforming or    -   vacuum forming or    -   pressing or    -   hot moulding or    -   cold moulding or    -   compression moulding or    -   injection moulding.

In a preferred, thermoforming embodiment of the method of the invention,the material is heated to a temperature that is near to the softeningtemperature of the material, so that thermoforming of the material ispossible, but is below the melting point of the material, so that thephysical integrity of the material is maintained. Thermoforming of theshaped lens blanks is then carried out through application of physicalforce to the heated material. The physical force might be applied bycompressing the material between two forms or platens.

In some preferred embodiments, the physical forming step B uses moulds.The material is placed between the moulds and these are pressed togetherto form said plurality of shaped lens blanks.

Further desirable features include the application of high energy(electron beam irradiation or gamma irradiation or microwave irradiationor ultraviolet irradiation) to sterilise either the lens blanks or thelenses.

In some further embodiments, the shaped lens blanks are transferred to aplurality of final packs. These final packs may be pre-sterilised. Theymay also contain the aseptic or sterile solution, which acts to hydratethe lenses in step C. In some such embodiments the material of theshaped lens blanks may undergo a chemical reaction, such as hydrolysis,in the final pack.

In a particularly preferred embodiment, all process steps after step Bare carried out without further human contact or handling. The methodmay thus be automated or semi-automated to run in a continuous orsemi-continuous manner.

In some embodiments, quality control inspections are carried out on theshaped lens blanks only. These inspections may be either visual or mayuse an optical system.

The invention also provides a method of producing a plurality ofophthalmic lenses, which comprises (a) providing a substantiallyuncrosslinked polymer, comprising crosslinkable groups; (b) physicallyforming this polymer into a plurality of ophthalmic lenses; and (c)applying high energy to the plurality of ophthalmic lenses thuscrosslinking the polymer to a predetermined, desired crosslink density.

In a preferred embodiment of the apparatus of the invention, the formingmeans comprises a plurality of forms or platens arranged so that theypress together to form the sheet of material into a plurality of shapedlens blanks. This plurality of forms or platens may be provided withheating means to heat the sheet of material to make the forming processeasier.

In some desirable embodiments, the plurality of platens are removablyconnectable with a plurality of male and female inserts. These male andfemale inserts are formed to appropriate shapes to form the shaped lensblanks to desired optical specifications. The inserts may be arrangedsuch that pressure (either positive or negative) may be applied throughthem.

In preferred embodiments of the apparatus of the invention, theapparatus further comprises packaging means for transferring said shapedlens blanks into final packs. This packaging means may be arranged tocarry out packaging in a substantially sterile environment.

In particularly preferred embodiments, the apparatus of the inventionalso comprises a removing means for removing the shaped lens blanks fromthe sheet of material and for forming the circumferential edges of theshaped lens blanks. This removing means may be a laser cutting meanssuch as a CO2 laser.

Some preferred embodiments of the apparatus provided by the inventionalso comprise high energy application means for applying high energy tothe shaped lens blanks and/or to soft contact lenses formed from theshaped lens blanks. This high energy application means could be anelectron beam irradiation means.

The current invention has many advantages over prior art productionmethods for ophthalmic lenses:

When using the current invention, there is no loss of precision in lensshape due to allowances that must be made in prior art methods both forshrinkage in the moulds as they cool and for shrinkage in initialmonomer volume due to polymerisation (typically a shrinkage of roughly16% which is very difficult to control accurately).

When using the current invention, there is no need to store and maintainan inventory of single-use moulds, which are not currently in use.

Since there is no need for producing disposable moulds, which are notpart of the final product, the current invention produces a dramaticreduction in waste material.

Due to using more easily-controllable process steps, lenses producedusing the current invention have an improved accuracy of lens power,improved surface quality and improved power consistency vis-à-vis thoseproduced using prior art methods.

Some particular embodiments of the current invention provide improvedsterilisation, packaging and in-line inspection steps over prior artmethods of production. These improvements can also lead to a reducedmanufacturing area requirement.

Compared to known methods of using reusable glass moulds, the currentinvention has the advantage that mould washing and inspections for mouldcleanliness is not required as frequently.

In the known methods which use curing by UV alone, UV-absorbing agentscannot be incorporated into lenses, since these then inhibit thepolymerisation process. In the current invention, non-UV forms ofirradiation may be employed when it is desired to create lensescontaining such UV-absorbing agents.

Other aspects and advantages of the invention will be clear from a studyof the following detailed description and drawings in which a particularembodiment of the invention is described consisting of a manufacturingprocess for contact lenses, wherein a contact lens is used as aparticular example of an ophthalmic lens and e-beam irradiation is usedas a particular example of a means of application of high energy.

BRIEF DESCRIPTION OF DRAWING

FIG. 1: A schematic diagram of a contact lens manufacturing apparatusaccording to an embodiment of the invention

DETAILED DESCRIPTION

FIG. 1 shows a schematic representation of an embodiment of theinvention. A roll of polymer in the form of sheet, 1, is provided and istransported to a thermoforming area, 14. Prior to entering thethermoforming area the polymer sheet is inspected by means of anautomatic vision system, 2, for significant defects, such as tears, thatwould result in an unsatisfactory final product.

The polymer may be Mowiol® (a material made by Clariant GmbH)—acopolymer of polyvinyl alcohol and polyvinyl acetate where the degree ofhydrolysis, as measured by saponification, is at least 96% mol based onthe original polyvinyl alcohol.

The polymer sheet is heated to a temperature where it is easy to shapethe polymer into the desired shape as defined by inserts on the mouldingplatens, 3 and 9, in the thermoforming process and yet the polymer sheetstill retains sufficient strength for it to be manipulated through theprocess.

The polymer sheet is then passed through the thermoforming area whereplatens, 3 and 9, containing optical quality inserts (not shown), shapethe polymer sheet into the desired form. Depending on the properties ofthe polymer sheet, the inserts and the platens may be cooled or heatedas required to obtain the required flow and optical clarity in theshaped part. The use of pressure or vacuum through the platens orinserts may also be used to achieve the desired shape. The opticalinserts and their bodies, which fit into the platen, are so designedthat the formed parts are not fully detached from the original polymersheet and so that after the forming process has been completed theformed parts are moved forward with the polymer sheet, 12.

The formed parts are then inspected by means of an automated visionsystem, 4, for defects. The polymer sheet with formed parts may then bestored for use in the future or processed immediately as a continuous orsemi-continuous process by passing it through a sterilising electronbeam at station 5.

If the polymer provided was not fully crosslinked, then the exposure ofthe polymer sheet and the formed parts to an electron beam may be socontrolled that the polymer becomes as crosslinked as is required aswell as sterile as is required. The formed parts are separated from thepolymer sheet and deposited into final packages within a sterileenvironment—schematically shown as occurring at station 5 in FIG. 1,although it is to be noted that packaging may occur at a separatestation from electron beam irradiation (not shown).

The final packages 15 are manufactured and/or treated at station 6 sothat they are effectively sterile and are maintained within anenvironment that keeps them, and the formed parts, sterile. The finalpackages are transported, 13, to a position to allow transfer of theformed parts into the final packages. The final packages holding theformed parts are transported within the sterile environment to a dosingstation, 7, where aseptic or sterile packaging/hydration solution isadded—controlled to be at a temperature below the temperature at whichthe polymer becomes water-soluble. The final packages, solution andformed parts are then sealed at station, 8, also within the sterilearea, with a sterile foil before leaving the process area for finallabelling.

“Ophthalmic lenses”, as used herein, refers to any medical or visioncorrection devices that are used in the ocular environment, includingcontact lenses, intraocular lenses, corneal onlays and inlays, oculardrug delivery devices, ocular wound healing devices and the like.

A crosslinking portion of the lens production process involves theexposure of a dry lens shape made from the polymer to a high energysource. “High energy”, as used herein, refers to many different formsand includes sources that generate, but is not limited to, thermal,I.R., U.V., microwave, gamma, ultrasonic and electron beam radiation.

“Crosslinking”, as used herein, is used to describe the process in whicha soluble polymer is converted into an insoluble form through theformation of bonds, i.e. crosslinks, between the polymer chains. It willbe obvious to those skilled in the art that the insoluble form may, inaddition to crosslinked structures, contain structures known as graftedpolymers or entangled polymers.

One purpose of crosslinking, as used herein, is to permit thecrosslinked dry lens to form a stable wet lens, as required by thedesign, and in doing so provide power correction to a wearer.

For polymers that are water-soluble the crosslinked polymer is known asa hydrogel.

“Polymer”, as used herein, refers to the material from which the initiallens shape is produced and includes copolymers, mixtures of polymers,interpenetrating network systems, polymer systems that are alreadypartially crosslinked, polymer to which additives have been added toassist in the crosslinking reaction, to reduce UV transmission, fortherapeutic purposes, to add colour for cosmetic reasons and the like.

The energy source and radiation used for any crosslinking may vary,together with time of exposure, depending on the polymer composition andthe properties required. In one preferred example of an ophthalmic lens,that of a hydrated contact lens, the final lens may comprise watercontent from 20 to 75%, by weight. It can be generally assumed that fora given polymer the crosslink density of the lens will control the watercontent of the lens, i.e. the greater the crosslink density the lowerthe water content.

In another example it is possible that the required levels of bothcrosslink density and sterility can be achieved simultaneously throughexposure to radiation.

It is generally desirable that any crosslinking process is achieved asquickly as possible, preferably in less than 10 minutes, more preferablyin less than 4 minutes, and even more preferably in less than oneminute. In some polymer formulations it may be necessary for there to bemore than one cycle to meet quality and performance requirements. At thesame time it is also necessary to ensure the safety of the personneloperating the process and of the general environment. For these reasonsthe level of energy used for the crosslinking process may be lower thanthat practically required for the necessary level of crosslinking in onepass; this is compensated for by multiple passes.

Where the radiation crosslinking is effected by exposure to an electronbeam or to gamma rays, additives, known as prorads, may be incorporatedinto the polymer at a level of 0.2 to 5% by weight for the purpose ofpromoting crosslinking. These compounds may be poly-functional vinyl orallyl compounds such as triallyl cyanurate, triallyl isocyanurate orpentaerithritol tetramethacrylate.

Radiation dosages will depend on the response of the polymer beingirradiated and on the level, if any, of prorad. Typical dosages will bein the range 20 to 800 kGy, preferably 20 to 500 kGy, e.g. 20 to 200 kGyand particularly 40 to 120 kGy.

The finished, packaged lens may also be sterilised by any otherappropriate means (e.g. ETO, gamma, steam etc.). Although the means ofsterilisation will have to be carefully selected so as not tosignificantly change the properties or performance of the lens orpackage.

1. A method of producing a plurality of soft contact lenses comprisingthe steps of: A. providing a sheet of solid, substantially dry material;B. forming said material into a plurality of shaped lens blanks throughcontrolled application of physical force to the material by compressionof the material between a plurality of form or platen pairs arranged inan array to simultaneously press together the material into a pluralityof shaped lens blanks in a process selected from the group consisting ofthermoforming, vacuum forming, pressing, hot moulding, cold moulding,and compression moulding; and C. hydrating said plurality of shaped lensblanks; wherein at least immediately subsequently to said physicalforming step B, said plurality of shaped lens blanks remain at leastpartially attached to the sheet of material and the sheet is used as atransport medium or carrying mechanism for said plurality of shaped lensblanks.
 2. A method of producing a plurality of soft contact lensesaccording to claim 1, wherein said sheet of solid substantially drymaterial is water soluble above a certain temperature, and formed intosaid plurality of shaped lens blanks at a temperature below said certaintemperature.
 3. A method of producing a plurality of soft contact lensesaccording to claim 2, in which said certain temperature is approximately50° C.
 4. A method of producing a plurality of soft contact lensesaccording to claim 2, in which said certain temperature is approximately65° C.
 5. A method of producing a plurality of soft contact lensesaccording to claim 1, in which the said material is chosen from thegroup consisting of polyvinyl alcohol or a copolymer of polyvinylalcohol and polyvinyl acetate or polyethylene-maleic-anhydride orpolymethyl-hydroxy-propyl-cellulose or copolymers of methyl acrylate orethyl acrylate with ethylene or their hydroxyl derivatives.
 6. A methodof producing a plurality of soft contact lenses according to claim 1, inwhich said material is a copolymer of polyvinyl alcohol and polyvinylacetate where the degree of hydrolysis, as measured by saponification,is at least 96% mol based on the original polyvinyl alcohol.
 7. A methodof producing a plurality of soft contact lenses according to claim 1, inwhich said material is a substantially uncrosslinked polymer comprisingcrosslinkable groups and in which, prior to the hydration step C, highenergy is applied to said plurality of shaped lens blanks, whereby saidpolymer is crosslinked to a predetermined, desired crosslink density. 8.A method of producing a plurality of soft contact lenses according toclaim 7, in which the material contains additives that react to theapplication of high energy to improve crosslinking efficiency.
 9. Amethod of producing a plurality of soft contact lenses according toclaim 7, in which the application of high energy involves irradiation ofthe plurality of shaped lens blanks by a form of high energy chosen fromthe group consisting of electron beam irradiation or gamma irradiationor microwave irradiation or ultraviolet irradiation or infraredirradiation or thermal irradiation or ultrasound irradiation.
 10. Amethod of producing a plurality of soft contact lenses according toclaim 1, wherein said plurality of shaped lens blanks are fully removedfrom the sheet at a stage after step B by the use of a laser cuttingdevice.
 11. A method of producing a plurality of soft contact lensesaccording to claim 1, in which said physical forming step B comprisesthe following substeps: B.1 heating said material to a temperature that:a) is near to the softening temperature of the material, wherebythermoforming of said material is possible, but b) is below the meltingpoint of said material, whereby the physical integrity of said materialis maintained; and B.2 thermoforming said plurality of shaped lensblanks through application of physical force to said material.
 12. Amethod of producing a plurality of soft contact lenses according toclaim 11, in which said thermoforming sub-step involves compression ofthe material between two forms or platens.
 13. A method of producing aplurality of soft contact lenses according to claim 1, in which thephysical forming step B involves the use of moulds and said material isplaced between said moulds which are pressed together to form saidplurality of shaped lens blanks.
 14. A method of producing a pluralityof soft contact lenses according to claim 1, in which high energy isapplied to said plurality of shaped lens blanks and/or to said pluralityof soft contact lenses in order to sterilise them.
 15. A method ofproducing a plurality of soft contact lenses according to claim 14, inwhich the application of high energy involves irradiation by a form ofhigh energy chosen from the group consisting of electron beamirradiation or gamma irradiation or microwave irradiation or ultravioletirradiation.
 16. A method of producing a plurality of soft contactlenses according to claim 1, which comprises the further step of: D.transferring the plurality of shaped lens blanks to a plurality of finalpacks.
 17. A method of producing a plurality of soft contact lensesaccording to claim 16, in which, before the transferring step D, thefinal packs are sterilised.
 18. A method of producing a plurality ofsoft contact lenses according to claim 17, in which, either before orafter the transferring step D, aseptic or sterile solution is added tothe sterile final packs which solution acts to hydrate the lenses instep C.
 19. A method of producing a plurality of soft contact lensesaccording to claim 16, in which the material of the shaped lens blanksundergoes a chemical reaction in the final packs.
 20. A method ofproducing a plurality of soft contact lenses according to claim 1, inwhich all process steps subsequent to step B are carried out withoutfurther human contact or handling.
 21. A method of producing a pluralityof soft contact lenses according to claim 1, which method is automatedor semi-automated to run in a continuous or semi-continuous manner. 22.A method of producing a plurality of soft contact lenses according toclaim 1, which further involves quality control inspections on theshaped lens blanks only.
 23. A method of producing a plurality of softcontact lenses according to claim 22, which involves either visualquality control inspections or quality control inspections using anoptical system.
 24. A method of producing a plurality of soft contactlenses according to claim 19, in which the material undergoes ahydrolysis reaction in the final packs.